Multi-modal Single-Cell Analysis Reveals Brain Immune Landscape Plasticity during Aging and Gut Microbiota Dysbiosis.

Phenotypic and functional plasticity of brain immune cells contribute to brain tissue homeostasis and disease. Immune cell plasticity is profoundly influenced by tissue microenvironment cues and systemic factors. Aging and gut microbiota dysbiosis that reshape brain immune cell plasticity and homeostasis has not been fully delineated. Using Cellular Indexing of Transcriptomes and Epitopes by sequencing (CITE-seq), we analyze compositional and transcriptional changes of the brain immune landscape in response to aging and gut dysbiosis. Discordance between canonical surface-marker-defined immune cell types and their transcriptomes suggest transcriptional plasticity among immune cells. Ly6C+ monocytes predominate a pro-inflammatory signature in the aged brain, while innate lymphoid cells (ILCs) shift toward an ILC2-like profile. Aging increases ILC-like cells expressing a T memory stemness (Tscm) signature, which is reduced through antibiotics-induced gut dysbiosis. Systemic changes due to aging and gut dysbiosis increase propensity for neuroinflammation, providing insights into gut dysbiosis in age-related neurological diseases.

CNS-Native Myeloid Cells Drive Immune Suppression in the Brain Metastatic Niche through Cxcl10.

Brain metastasis (br-met) develops in an immunologically unique br-met niche. Central nervous system-native myeloid cells (CNS-myeloids) and bone-marrow-derived myeloid cells (BMDMs) cooperatively regulate brain immunity. The phenotypic heterogeneity and specific roles of these myeloid subsets in shaping the br-met niche to regulate br-met outgrowth have not been fully revealed. Applying multimodal single-cell analyses, we elucidated a heterogeneous but spatially defined CNS-myeloid response during br-met outgrowth. We found Ccr2+ BMDMs minimally influenced br-met while CNS-myeloid promoted br-met outgrowth. Additionally, br-met-associated CNS-myeloid exhibited downregulation of Cx3cr1. Cx3cr1 knockout in CNS-myeloid increased br-met incidence, leading to an enriched interferon response signature and Cxcl10 upregulation. Significantly, neutralization of Cxcl10 reduced br-met, while rCxcl10 increased br-met and recruited VISTAHi PD-L1+ CNS-myeloid to br-met lesions. Inhibiting VISTA- and PD-L1-signaling relieved immune suppression and reduced br-met burden. Our results demonstrate that loss of Cx3cr1 in CNS-myeloid triggers a Cxcl10-mediated vicious cycle, cultivating a br-met-promoting, immune-suppressive niche.

Target-Enriched Endosymbiont Sequencing (TEEseq): A New High-Throughput Sequencing Approach Applied to the Comprehensive Characterization of Endosymbionts.

Intracellular bacteria are ubiquitous in the insect world, with perhaps the best-studied example being the alphaproteobacterium, Wolbachia. Like most endosymbionts, Wolbachia cannot be cultivated outside of its host cells, hindering traditional microbial characterization techniques. Furthermore, multiple Wolbachia strains can be present within a single host, and certain strains can be present in densities below the detection limit of current methods. To date, Wolbachia has most commonly been studied using polymerase chain reaction (PCR) amplification and Sanger DNA sequencing by targeting specific genes in the bacterium's genome. PCR amplification and Sanger sequencing of multiple Wolbachia strains requires analysis of individually cloned sequences, which is resource and labor intensive. To help mitigate these difficulties, we present a modified double digest restriction site associated DNA sequencing (ddRADseq) approach to target and sequence in parallel multiple genes by adding restriction enzyme recognition sites to gene-specific PCR primers. Adopting this strategy allows us to uniquely tag and sequence amplicons from multiple hosts simultaneously on an Illumina MiSeq platform. Our approach represents an efficient and cost-effective method to characterize multiple target genes in population surveys.

The transcriptomic and proteomic responses of Daphnia pulex to changes in temperature and food supply comprise environment-specific and clone-specific elements.

BACKGROUND: Regulatory adjustments to acute and chronic temperature changes are highly important for aquatic ectotherms because temperature affects their metabolic rate as well as the already low oxygen concentration in water, which can upset their energy balance. This also applies to severe changes in food supply. Thus, we studied on a molecular level (transcriptomics and/or proteomics) the immediate responses to heat stress and starvation and the acclimation to different temperatures in two clonal isolates of the model microcrustacean Daphnia pulex from more or less stressful environments, which showed a higher (clone M) or lower (clone G) tolerance to heat and starvation. RESULTS: The transcriptomic responses of clone G to acute heat stress (from 20 °C to 30 °C) and temperature acclimation (10 °C, 20 °C, and 24 °C) and the proteomic responses of both clones to acute heat, starvation, and heat-and-starvation stress comprised environment-specific and clone-specific elements. Acute stress (in particular heat stress) led to an early upregulation of stress genes and proteins (e.g., molecular chaperones) and a downregulation of metabolic genes and proteins (e.g., hydrolases). The transcriptomic responses to temperature acclimation differed clearly. They also varied depending on the temperature level. Acclimation to higher temperatures comprised an upregulation of metabolic genes and, in case of 24 °C acclimation, a downregulation of genes for translational processes and collagens. The proteomic responses of the clones M and G differed at any type of stress. Clone M showed markedly stronger and less stress-specific proteomic responses than clone G, which included the consistent expression of a specific heat shock protein (HSP60) and vitellogenin (VTG-SOD). CONCLUSIONS: The expression changes under acute stress can be interpreted as a switch from standard products of gene expression to stress-specific products. The expression changes under temperature acclimation probably served for an increase in energy intake (via digestion) and, if necessary, a decrease in energy expenditures (e.g, for translational processes). The stronger and less stress-specific proteomic responses of clone M indicate a lower degree of cell damage and an active preservation of the energy balance, which allowed adequate proteomic responses under stress, including the initiation of resting egg production (VTG-SOD expression) as an emergency reaction.

Conserved transcriptional responses to cyanobacterial stressors are mediated by alternate regulation of paralogous genes in Daphnia.

Despite a significant increase in genomic data, our knowledge of gene functions and their transcriptional responses to environmental stimuli remains limited. Here, we use the model keystone species Daphnia pulex to study environmental responses of genes in the context of their gene family history to better understand the relationship between genome structure and gene function in response to environmental stimuli. Daphnia were exposed to five different treatments, each consisting of a diet supplemented with one of five cyanobacterial species, and a control treatment consisting of a diet of only green algae. Differential gene expression profiles of Daphnia exposed to each of these five cyanobacterial species showed that genes with known functions are more likely to be shared by different expression profiles, whereas genes specific to the lineage of Daphnia are more likely to be unique to a given expression profile. Furthermore, while only a small number of nonlineage-specific genes were conserved across treatment type, there was a high degree of overlap in expression profiles at the functional level. The conservation of functional responses across the different cyanobacterial treatments can be attributed to the treatment-specific expression of different paralogous genes within the same gene family. Comparison with available gene expression data in the literature suggests differences in nutritional composition in diets with cyanobacterial species compared to diets of green algae as a primary driver for cyanobacterial effects on Daphnia. We conclude that conserved functional responses in Daphnia across different cyanobacterial treatments are mediated through alternate regulation of paralogous gene families.

Differential transcriptomic responses of ancient and modern Daphnia genotypes to phosphorus supply.

Little is known about the role of transcriptomic changes in driving phenotypic evolution in natural populations, particularly in response to anthropogenic environmental change. Previous analyses of Daphnia genotypes separated by centuries of evolution in a lake using methods in resurrection ecology revealed striking genetic and phenotypic shifts that were highly correlated with anthropogenic environmental change, specifically phosphorus (P)-driven nutrient enrichment (i.e. eutrophication). Here, we compared the transcriptomes of two ancient (~700-year-old) and two modern (~10-year-old) genotypes in historic (low P) and contemporary (high P) environmental conditions using microarrays. We found considerable transcriptomic variation between 'ancient' and 'modern' genotypes in both treatments, with stressful (low P) conditions eliciting differential expression (DE) of a larger number of genes. Further, more genes were DE between 'ancient' and 'modern' genotypes than within these groups. Expression patterns of individual genes differed greatly among genotypes, suggesting that different transcriptomic responses can result in similar phenotypes. While this confounded patterns between 'ancient' and 'modern' genotypes at the gene level, patterns were discernible at the functional level: annotation of DE genes revealed particular enrichment of genes involved in metabolic pathways in response to P-treatments. Analyses of gene families suggested significant DE in pathways already known to be important in dealing with P-limitation in Daphnia as well as in other organisms. Such observations on genotypes of a single natural population, separated by hundreds of years of evolution in contrasting environmental conditions before and during anthropogenic environmental changes, highlight the important role of transcriptional mechanisms in the evolutionary responses of populations.

Functional genomics of intraspecific variation in carbon and phosphorus kinetics in Daphnia.

Understanding how the genome interacts with the environment to produce a diversity of phenotypes is a central challenge in biology. However, we know little about how traits involved in nutrient processing interact with key ecological parameters, such as the supply of mineral nutrients, particularly in animals. The framework of ecological stoichiometry uses information on the content of key elements such as carbon (C) and phosphorus (P) in individuals to predict the success of species. Nevertheless, intraspecific variation in content and the underlying mechanisms that generate such variation has been poorly explored. We studied two genotypes (G1 and G2) of Daphnia pulex that exhibit striking genotype × environment (G × E) interaction in response to shifts in dietary stoichiometry (C:P). G1 had higher fitness under C:P ∼ 100 diet, while G2 performed better in C:P ∼ 800. Dual (14) C/(33) P radiotracer assays show that G1 was more efficient in C processing, while G2 was more efficient in P use. Microarrays revealed that after 3 days of incubation, the genotypes differentially expressed ∼ 25% (7,224) of the total genes on the array under C:P ∼ 100 diet, and ∼ 30% (8,880) of genes under C:P ∼ 800. These results indicate large differences in C and P use between two coexisting genotypes. Importantly, such physiological differences can arise via differential expression of the genome due to alterations in dietary stoichiometry. Basic frameworks such as ecological stoichiometry enable integration of physiological and transcriptomic data, and represent initial steps toward understanding the interplay between fundamental ecological parameters such as nutrient supply and important evolutionary processes such as G × E interactions.

Fine-scale mapping of the Nasonia genome to chromosomes using a high-density genotyping microarray.

Nasonia, a genus of four closely related parasitoid insect species, is a model system for genetic research. Their haplodiploid genetics (haploid males and diploid females) and interfertile species are advantageous for the genetic analysis of complex traits and the genetic basis of species differences. A fine-scale genomic map is an important tool for advancing genetic studies in this system. We developed and used a hybrid genotyping microarray to generate a high-resolution genetic map that covers 79% of the sequenced genome of Nasonia vitripennis. The microarray is based on differential hybridization of species-specific oligos between N. vitripennis and Nasonia giraulti at more than 20,000 markers spanning the Nasonia genome. The map places 729 scaffolds onto the five linkage groups of Nasonia, including locating many smaller scaffolds that would be difficult to map by other means. The microarray was used to characterize 26 segmental introgression lines containing chromosomal regions from one species in the genetic background of another. These segmental introgression lines have been used for rapid screening and mapping of quantitative trait loci involved in species differences. Finally, the microarray is extended to bulk-segregant analysis and genotyping of other Nasonia species combinations. These resources should further expand the usefulness of Nasonia for studies of the genetic basis and architecture of complex traits and speciation.

Identification of maternally-loaded RNA transcripts in unfertilized eggs of Tribolium castaneum.

BACKGROUND: Maternal RNAs play a critical role in early development. Variation in the diversity and levels of maternally derived gene transcripts may be central to the origin of phenotypic novelty -- a longstanding problem in evolution and development. By studying maternal transcriptomes within and between divergent species, a better understanding of the evolutionary forces acting on maternal RNA allocation is possible. RESULTS: We present the first maternal transcriptome of the red flour beetle, Tribolium castaneum. Using a tiled whole-genome microarray, we found that 58.2% of T. castaneum genes are maternally loaded into eggs. Comparison of known Drosophila melanogaster maternal genes to our results showed widespread conservation of maternal expression with T. castaneum. Additionally, we found that many genes previously reported as having sex or tissue specific expression in T. castaneum were also maternally loaded. Identification of such pleiotropy is vital for proper modeling and testing of evolutionary theory using empirical data. The microarray design also allowed the detection of 2315 and 4060 novel transcriptionally active regions greater in length than 100 bp in unfertilized and fertilized T. castaneum eggs, respectively. These transcriptionally active regions represent novel exons of potentially unknown genes for future study. CONCLUSIONS: Our results lay a foundation for utilizing T. castaneum as a model for understanding the role of maternal genes in evolution.

How do consumers deal with stoichiometric constraints? Lessons from functional genomics using Daphnia pulex.

Disaccord between the supply and demand of energy (carbon, C) and certain material elements (e.g. phosphorus, P) across trophic levels is common in most ecosystems and impacts the strength of trophic interactions and ecosystem functions such as productivity and nutrient recycling. Yet, we know little about mechanisms operating at the lower levels of biological organization that drive such higher-level ecological processes. Such information should help refine theories integrating biological processes at multiple levels of organization. Understanding the expression and functions of genes that underlie (to a large degree) physiological adjustments made by organisms to stoichiometric imbalances at trophic interfaces is a first step in this enterprise. Here, we investigate adjustments in gene expression to varying supply and demand of phosphorus relative to other dietary components in the keystone limnetic herbivore, Daphnia pulex. Daphniids were fed an algal diet of either LoC-HiP (molar C:P ∼100) or HiC-LoP (molar C:P ∼900) for 5 days, resulting in significant growth reductions under HiC-LoP conditions. Microarrays measured the transcriptional regulation of 8217 annotated protein-coding genes under contrasting dietary conditions and revealed 1818 differentially expressed (DE) genes; 19% are genes unique to the Daphnia lineage. We mapped DE genes onto a global chart of metabolic pathways to obtain a systems-level perspective on the responses to stoichiometric imbalances. Daphnia differentially regulated pathways were involved in sequestering limiting elements, and in dealing with the products of metabolic adjustments that may be triggered by nutrient stress in primary producers. Functional genomics at trophic interfaces illuminate the complexity of processes underlying stoichiometric constraints on energy and nutrient fluxes in ecosystems.